Catalyst switch strategy enabled a single polymer with five different crystalline phases

Well-defined multicrystalline multiblock polymers are essential model polymers for advancing crystallization physics, phase separation, self-assembly, and improving the mechanical properties of materials. However, due to different chain properties and incompatible synthetic methodologies, multicrystalline multiblock polymers with more than two crystallites are rarely reported. Herein, by combining polyhomologation, ring-opening polymerization, and catalyst switch strategy, we synthesized a pentacrystalline pentablock quintopolymer, polyethylene-b-poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(L-lactide)-b-polyglycolide (PE-b-PEO-b-PCL-b-PLLA-b-PGA). The fluoroalcohol-assisted catalyst switch enables the successful incorporation of a high melting point polyglycolide block into the complex multiblock structure. Solid-state nuclear magnetic resonance spectroscopy, X-ray diffraction, and differential scanning calorimetry revealed the existence of five different crystalline phases.


Instruments
Liquid-state Nuclear Magnetic Resonance Spectroscopy: Bruker AV600 MHz nuclear magnetic resonance (NMR) spectrometer was used to record 1 H or 13 C NMR spectra at 80 °C or 60 °C using deuterated toluene (Tol-d8) or deuterated hexafluoroisopropanol (HFIP-d2) with tetramethylsilane (TMS) as the internal standard.The diffusion-ordered spectroscopy (DOSY) is

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performed on a Bruker 600 MHz liquid NMR spectrometer at 298.1 K. 32 gradient strengths varying linearly between 5% and 100% of the maximum gradient strength and 16 scans per increment were used to construct the decay function.D20 = 1.2000 s, P30 = 1500.00µs.The phase of the original data is adjusted manually and the baseline is smoothed via TopSpin 4.2.0.Bayesian method is used for processing the raw spectra.Resolution factor = 5.00 and repetitions = 3. were conducted on a Bruker AVANCE III spectrometer using a 3.2 mm MAS probe.The experiments were performed according to the following scheme: 90° proton pulse, t1 evolution period, CP to 13 C, and detection of the 13 C magnetization under TPPM decoupling.For the crosspolarization step, a ramped radio frequency (RF) field centered at 75 kHz was applied to the protons, while the 13 C channel RF field was matched to obtain an optimal signal.A total of 64 t1 increments with 1024 scans each were collected.The sample spinning frequency was 8 kHz.Using a short contact time (500 µs) for the CP step, the polarization transfer in the dipolar correlation experiment was verified to be selective for the first coordination sphere to lead to correlations only between pairs of attached 1 H− 13 C spins (C−H directly bonded).

Solid
For 13 C CP−MAS NMR experiments, the following sequence was used: 90° pulse on the proton (pulse length 2.5 µs), then a cross-polarization step with a contact time of typically 1 ms, and finally acquisition NMR signal under high-power proton decoupling.The delay between the scans was set to 4 s to allow the complete relaxation of the 1 H nuclei, and the number of scans ranged between 1024 and 4096 for 13 C and 32 for 1 H.An exponential apodization function corresponding to a line broadening of 80 Hz was applied prior to the Fourier transformation.

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The 1D insensitive nuclei enhanced by polarization transfer (INEPT) spectra were recorded using a 2 s recycle delay, 20 ms acquisition time, and accumulation of 4k scans. 1 H and 13 C pulses were applied with a field strength of 70 and 50 kHz, respectively.
The solid-state 1 H− 13 C WISE 2D NMR spectrum was performed on Bruker AVANCE III spectrometers operating at 600 MHz resonance frequencies using a 3.2 mm MAS probe.A MAS of 6 kHz was applied in all experiments.The increment time t1 was set to 5 µs. the contact time was 1 ms.

SEC:
For polyethylene precursor, high-temperature size exclusion chromatography measurements were carried out on the Agilent 1260 II infinity High-Temperature SEC (Agilent Technologies) with 2  PLgel 10 m MIXED-B, 300  7.5 mm columns.TCB was used as an eluent at a temperature of 150 °C.For PE1.5k-based multiblock polymers, size exclusion chromatography (SEC) measurements equipped with a refractive index (RI) detector were conducted in THF at 50 °C using two identical PLgel MIXED-C columns (5 m) at a flow rate of 1.0 mL min -1 (polystyrene standard).
DSC: Differential scanning calorimetry (DSC) measurements were performed at a heating/cooling rate of 10 °C min -1 on a Discovery 2500 DSC machine (TA instruments) under nitrogen with a flow rate of 50 mL min -1 .A heating/cooling rate of 5 °C min -1 may be needed for samples with a PLLA block.
TGA: Thermogravimetric analysis (TGA) was conducted on a Discovery 5500 TGA analyzer (TA Instruments) under nitrogen with a flow rate of 50 mL min -1 and a heating rate of 10 °C min -1 .
XRD: Wide-angle X-ray diffractions were carried out on Bruker D2 Phaser XRD spectrometry.The sample was pre-annealed at 180 °C (230 °C for samples with PGA block) for 5 minutes and slowly cooled down to 0 °C (~ 2 °C min -1 ).
[e] Determined by 1 H NMR of the purified sample at 60 ºC (600 MHz, toluene-d8), except for the PE-OH7k precursor, where a higher temperature of 90 ºC was used.
[h] The sample is not fully soluble, even in the mixture of HFAB and toluene at high temperatures.
-state Nuclear Magnetic Resonance Spectroscopy.One-dimensional 1 H magic angle spinning (MAS) and 13 C cross-polarization (CP) MAS solid-state NMR spectra were recorded on Bruker AVANCE III spectrometers operating at 600 MHz resonance frequencies for 1 H utilizing a 3.2 mm double-resonance probe.Dry nitrogen gas was utilized for sample spinning to prevent the degradation of the samples.NMR chemical shifts are reported with respect to the external references TMS and adamantane.